I don't expect any of what I suggest to ever make it in to your game, but if they do, they do.
I will attempt to add in as many as I can, but prioritizing what appears to be the most meaningful first.
Assuming the hammers work eventually, it won't actually take THAT long to uncover the whole map in Expansion despite you wanting it to be a slow, endgame feature.
That expansion location represents a single sector of virtually infinite sectors. The main idea is exclusive rewards from beating the sector compared to other parts of the game.
I also wonder if you plan to add armies to Expansion so that the areas that are populated by other forces can be defeated and built upon.
There is combat in expansion, but perhaps you mean something else. (For combat it requires a specific building).
A new map but with all or a percentage of your existing supplies? Some new buildings, features or currencies? A crossover potential between Expansion and Sanctum?
There is an exclusive reward for beating the sector, but long-term I'd like that system to become diplomatic, and universally influential, but that will require proper story systems I think (working on it, but it will take considerable time, I might try prioritizing pushing out a barebones foundation though for testing).
I don't really know what I'm getting at here so I'll stop writing before this turns into a novel or I just decide to delete rather than send. Iike to write. You have probably noticed this by now.
I enjoy reading these.